1. Field of the Invention
The present invention relates generally to a continuous ion exchange apparatus, and more particularly to a two-bed type or other continuous ion exchange apparatus, e.g., for use in the production of high purity water such as deionized water in which the feed water is upwardly passed through an ion adsorption zone, a washing zone, a resin regeneration zone sequentially segmented from the lower portion to the upper portion within a single column filled with an ion exchange resin while the ion exchange resin is transferred downward or in the opposite direction to the feed water passage direction in such a manner that the ion exchange resin which has been regenerated and washed can be continuously supplied into the adsorption zone from the upper portion, thereby executing a substantially continuous ion exchange treatment of the feed water passing through the adsorption zone.
2. Description of the Related Arts
A typical apparatus for the production of high purity water such as deionized water hitherto known is a fixed-bed type ion exchange apparatus in which an ion exchange treatment and a regeneration treatment by the passage of a regenerant are alternately performed. However, the apparatus has a poor productivity due to the interruption of the passage of feed water during the regeneration treatment, and hence is unsuitable for the application requiring a successive supply of water. For this reason, various apparatuses allowing a continuous ion exchange treatment without being interrupted have been put into practical use.
The continuous ion exchange apparatuses are classified into a fluidized bed type and a moving bed type, the latter being industrially commonly used and subgrouped into a mixed bed type and a multiple-bed type.
The mixed bed type continuous ion exchange apparatus comprises an exhaustion (adsorption) column mixedly filled with cation exchange resin and anion exchange resin, a resin separation column, and a couple of regeneration columns. In this apparatus, feed water is introduced into the exhaustion column through the lower portion thereof, to force the mixed resin bed toward the top of the exhaustion column to form a fixed bed, subjecting the feed water passing therethrough to an ion exchange treatment. This will allow a gradual upward movement of the ion exchange zone in which ion exchange takes place within the mixed resin bed through which the feed water passes. The resins exhausted with impurity ions (the resins whose ion exchange ability to adsorb impurity ions have been spent) are transferred as a slurry through the bottom of the exhaustion column to the resin separation column in which the resin slurry is backwashed and separated into the cation exchange resin and anion exchange resin, and then sent to their respective regeneration columns. The ion exchange resins regenerated in these columns are metered and mixed, and then fed to the top of the interior of the exhaustion column while interrupting (usually about several ten seconds) the passage of feed water through the exhaustion column, thereby accomplishing a substantially continuous ion exchange.
On the other hand, the multiple-bed type continuous ion exchange apparatus is represented by a deionized water production unit called, for example, two-bed type without or with a decarbonator. In the two-bed type without a decarbonator, the feed water is passed through a cation column (hereinafter referred to also as "column C") filled with a cation exchange resin, and then passed through an anion column (hereinafter referred to also as "column A") filled with an anion exchange resin. The two-bed type continuous ion exchange apparatus with a decarbonator further comprises a decarbonator interposed between the columns C and A for the purpose of reducing the ion load on the column A.
The above-described multiple-bed type continuous ion exchange apparatus, for example, the two-bed type apparatus with a decarbonator may be actually called a two-bed seven-column type since in addition to the decarbonator column each of the columns C and A needs one regeneration column (for regenerating the cation or anion resin) plus a wash column (for washing the cation or anion resin after regeneration.) Such a number of columns (or vessels) entails a great deal of additional equipment such as piping and valves necessary for the resin transfer, which in turn results in an increased equipment cost, and a larger space for installation, and a complicated operation.
In contrast, the mixed bed type continuous ion exchange apparatus has an advantage over the multiple-bed type in the case where the quality of the feed water is comparatively good, the content of weak acidic components such as carbonic acid or silica (silicic acid) in the feed water is low, the quantity of the feed water to be treated is great, or the space for installation is restricted. Nevertheless, the mixed bed type apparatus has some drawbacks, for example, 1) it needs more alkaline regenerant than the multiple-bed type continuous ion exchange apparatus having a decarbonator since the anion exchange resin used for the mixed bet unit adsorbs bicarbonate ions and the like as well as the other anions, and 2) the cation exchange resin may be mixed into the anion exchange resin regeneration column due to insufficient separation of the cation exchange resin and the anion exchange resin within the resin separation column whereupon calcium ions or magnesium ions the cation exchange resin has adsorbed may become insoluble in the anion exchange resin regeneration column after the elution from the cation resin, thereby clogging a collector and so on. In this manner, the continuous ion exchange apparatuses which have been hitherto put into practice leave much to be desired irrespective of whether they are mixed bed type or multiple-bed type.
Apart from the above-described known continuous ion exchange apparatus, the present applicant has proposed a continuous ion exchange apparatus using thermally regenerable special ion exchange resins (see Japanese Patent Pub. No. 50379/1984). This continuous ion exchange apparatus utilizes the special properties of the thermally regenerable resins whose ion exchange capacity can be regenerated by hot water, to thereby execute both the ion exchange treatment and the regeneration treatment within a single treatment column.
The present inventor has considered, due to the speciality of the resin used, that the continuous ion exchange apparatus using the thermally regenerable resins will not be directly applicable to the continuous ion exchange apparatus using the ion exchange resins whose ion exchange abilities are recovered by ordinary acid or alkali. However, despite the shortcomings such for example as mixing of the regenerant into the treated water which may be caused by insufficient washing, deterioration in the washing efficiency which may be caused by the increase in the volume of washing water, or reduction in the recovery of the feed water, it has considerable advantages. For example, there is no need to separately provide any column for the regeneration since the ion exchange treatment and the regeneration can be carried out within a single column, contributing to the elimination or reduction of the drawbacks such for example as a larger space required for installation of the two-bed type apparatus described above. Thus, the present inventor has continued studying the wider application of the continuous ion exchange apparatus designed for thermally regenerable resins.